In a gear train, when more than one gear sits on a single shaft, the arrangement is called a

• A. Simple gear train
• B. Compound gear drive
• C. Planetary gear set
• D. Differential gear

Answer: (B)

This tests how gear trains are classified based on how gears are arranged on shafts. When more than one gear sits on a single shaft, those gears turn together as a unit. That creates a compound stage in the gear train, because you’re effectively combining two gear steps into one continuous shaft. This arrangement lets you achieve a different overall gear ratio than you would with separate gear pairs on separate shafts.

So the term for this setup is a compound gear drive. It’s distinct from a simple gear train, where each shaft carries only one gear; from a planetary gear set, which uses a sun gear, planet gears, and a ring gear with a carrier; and from a differential, which distributes torque between outputs.